Transplant-associated arteriosclerosis (TAA) is the major cause of death in recipients who survive more than one year after cardiac transplantation. TAA is characterized by infiltration of inflammatory cells followed by the formation of a diffuse, concentric neointima in which smooth muscle cells and lipid-laden macrophages accumulate. Cells of the immune system-particularly the macrophage-play a key role in TAA. Through uptake of oxidized lipids, elaboration of inflammatory cytokines, and release of proteolytic enzymes, activated macrophages are critical to TAA. The long-term objectives are to identify mechanisms regulating these processes. The pleiotropic growth factor, TGF-01, is an important regulator of cellular growth, differentiation, and immune modulation. Efforts to elucidate mechanisms by which TGF-beta1 mediates its functions have identified a number of effector proteins termed Smads. Although nine Smads have been identified, their role in macrophage biology has not been assessed. We found that a single member of the Smad family. Smad3-is critical for inhibiting markers of macrophage activation. This proposal aims to investigate the role of Smad3 in regulating activated macrophages and its role in the pathogenesis of TAA. Our data suggest that a novel mechanism is regulating Smad3's inhibitory function likely involving binding to an essential co-factor in macrophages. Thus, we propose to identify and characterize interaction partners for Smad3 in macrophages and assess how such factor(s) may affect Smad3's regulation on macrophage activation. To assess the effect of Smad3 on a broad range of macrophage effector functions, we will employ adenoviral strategies to overexpress both Smad3 and a dominant negative Smad3 in macrophages. Finally, to evaluate the in vivo role of Smad3, we will determine the contribution of Smad3 in the development of transplant arteriopathy using a mouse model of cardiac allograft transplantation in Smad3-/- recipient mice. Insight into the mechanism governing SmadYs role in inflammation may provide potential, therapeutic targets applicable to a number of inflammatory diseases.